CRN1, which encodes the yeast homologue of coronin, is an actin- and microtubule-associated protein (1). Crn1p contains five amino-terminal WD repeats which form a beta-propeller structure; a microtubule binding domain; and a carboxyl terminal alpha-helical coiled coil structure. Localization of Crn1p to cortical patches requires both its beta-propeller and coiled-coil domains (5, 6).

Crn1p binds actin filaments (F-actin) and cross-links F-actin to form long actin filament bundles (1). Crn1p also regulates the actin filament nucleation and branching activity of the Arp2/3 complex through interaction with the Arc35p subunit (3). The Arp2/3 complex by itself has weak actin nucleation activity and is activated by binding to the side of an actin filament or by association with activator proteins like Las17p and Abp1p (7). Crn1p inhibits de novo actin nucleation by the Las17p- and Abp1p-activated Arp2/3 complex by binding to the Arc35p subunit which stabilizes an open, inactive conformation of the Arp2/3 complex. This inhibitory role is observed only in the absence of preformed actin filaments. In the presence of preformed filaments, Crn1p restricts the activated-Arp2/3 complex to the sides of actin filaments and permits actin nucleation (3, 2, 8). crn1 null mutants display slow movement of actin cortical patches from the membrane into the cytoplasm (4) while overexpression of CRN1 results in defects in actin and microtubule organization (2).

Coronins are an evoluntionarily well conserved family of WD repeat proteins involved in actin cytoskeleton organization. The C. elegans POD-1 has also been shown to be involved in vesicular trafficking (reviewed in 6).

Last updated: 2008-03-07